Reflected-in beam paths for illumination of a specimen field are used in a wide variety of applications, and in particular in the medical field. Usually the illumination beam path is reflected into the main beam path of the microscope via a deflecting mirror or deflecting prism, which as a rule is mounted on the axis of the microscope's main beam path. This results in illumination of the specimen surface directly on the axis of a microscope's main beam path. If the illumination is applied laterally from the axis of the main beam path, this usually results in more or less undesirable shadowing.
For a number of applications, however, an illumination deviating from the observation axis is desirable. The Zeiss company achieves this, as is known from DE-A-40 28 605 and DE-A-197 28 035, by way of a second mirror. For ophthalmic surgery in particular, a so-called “zero-degree” illumination (“zero-degree” indicating illumination on the axis of the main beam path) is inclined at a small angle of e.g. 6 degrees in order to improve the visibility of the surgical field.
In a particular embodiment of the system for reflecting in illumination (cf. DE-A-196 50 773), the Möller company asserted the idea of introducing light directly into the observation beam paths.
In order to achieve partial darkening of the specimen field, stops are used as necessary in the illumination beam path (cf. U.S. Pat. No. 4,715,714 in this context). These are located, however, in the illumination location conjugated with the specimen field. Stops of this kind can be used, for example, to reduce the so-called “red reflection,” once again in ophthalmic surgery. In order deliberately to reduce tissue stress, other stops serve to exclude the light directed via the respective mirror.
The inventor has recognized that the known systems are disadvantageous in the following respects:                a) At present, continuous adaptation of the illumination angle in the radial and axial directions with respect to the microscope's main beam path is not possible.        b) Oblique illumination via two mirrors makes possible only predefined illumination angles in the radial direction with respect to the microscope's main beam path, thereby resulting in a limitation in contrast selection.        c) Reflection into the observation beam paths is suitable for illumination in narrow channels, but results on the one hand in poor contrast and on the other hand in solutions that are difficult to design.        d) Because the illumination is reflected into the convergent beam path, the arrangement as defined in DE-A-36 23 613 results in light loss and double images.        